Last week the Labour leader gave an Arsenal shirt to the EU's chief Brexit negotiator

66 per cent said Britain should definitely stay in the single market, with another 21 per cent saying we should probably keep membership of the body, even though that would prevent us from ending free movement.

Only 4.2 per cent of Labour activists want to leave the single market.

The situation is similar when it comes to the customs union - which stops Britain striking trade deals around the world - with 85 per cent of party members saying they would prefer to stay in.

A majority of Labour’s members are even keen to overturn the result of the Brexit referendum altogether.

78 per cent said it would be a good idea to hold a second vote on EU membership once the outcome of Theresa May’s negotiation is known.

Jeremy Corbyn - a longtime Eurosceptic - has vowed to honour the result of the referendum by quitting the EU and ending the immigration free-for-fall.

JEZ ANGER

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MERKEL BREXIT BOOST

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He told the Guardian: “Retaining the benefits of the single market and the customs union must be the priority for negotiations.”

But pro-EU backbencher Chuka Umunna called for a policy change, saying: “It is clear that Labour people want to see clear red water between Theresa May’s job-destroying Brexit and Labour’s position.

“Here is clear evidence that keeping membership of the single market and the customs union on the table in these negotiations is the best way Labour can distinguish itself and provide the strongest possible opposition to the Tories on Brexit.”

A pro-Remain backbencher today warned her colleagues that Labour would look like “liars” if they tried to sabotage the Government’s plans for Brexit.

Caroline Flint said that staying in the single market would be "EU membership in all but name" and insisted MPs could not “wriggle out” of honouring the referendum.

She said: “We cannot change tack or try to suggest that anything less than full membership of the single market and customs union is a hard Brexit.

"Those who aim to keep us in the single market know full well that this is EU membership in all but name.”